1. Field of the Invention
The present invention relates to a front cover assembly and a method of making the same and in particular, to a front cover assembly for a touch sensitive device that provides a watertight seal, infrared filtering and that is insensitive to ambient temperature variations.
2. Description of the Prior Art
One type of interactive computer system permits an operator to enter information into the computer by selectively touching points on the screen of a computer monitor or display device, such as a Cathode Ray Tube (CRT) or Liquid Crystal Display (LCD), upon which is displayed relevant information. One such touch input system provides an arrangement of radiation emitter and detector pairs, for example a plurality of light emitters (typically in the infrared range) arranged along one vertical side and one horizontal side of the display screen, and a plurality of detectors arranged along the other horizontal and vertical sides. The resulting rectangular arrangement of emitter and detector pairs produces a corresponding light beam grid over the display screen that when interrupted by the operator's finger or a pointer or other object, permits the touched screen location to be determined by the computer or display electronics. The computer can then relate the location to information being displayed at the touch screen location. The advantage of a touch screen is that the operator may simply touch the display object or portion of the display screen to select, highlight or otherwise input information.
In most environments, and in food service environments in particular, computers are subject to liquids, foods, grease, moisture, and other contaminants. This is particularly a problem in food services where cashiers are often required to consummate transactions as well as provide the customer with the purchased food and drink. The point of sale devices that the cashier uses to input transaction information are often subject to liquids, foods, grease, moisture from handling of the food and drink by the cashier and other contaminants incident to food service. These contaminants can be transferred to the point of sale device when the cashier inputs transaction related information (e.g., customer's order, amount tendered, etc . . . ). Furthermore, food and drink are often spilled or drip on to the device itself. Contamination of the display and/or display cover is particularly a problem in computer systems that use touch input. This is because the cashier is constantly touching the device, handling the food and drink and because the cashier's skin generates or secretes oil naturally. Thus, these touch devices need be cleaned frequently. Cleaning the front cover compounds the situation by subjecting the device to cleaning fluids, liquids and/or solutions. The cleaning fluids can cause additional reactions with the display elements. Thus, in order to operate properly in a harsh food service environment a permanent liquid tight seal is needed to protect sensitive electronic display elements.
Prior art techniques have attempted to solve this problem in several ways. Typically, a front cover for a touch screen would contain one or more gaskets. Not only do gaskets leak after exposure to harsh cleaning fluids but, they also require the use of additional assembly steps and the addition of the gasket(s) itself. The gasket must be attached and seated properly in order to function effectively. The use of gaskets requires multiple operations and parts which make front covers using gaskets expensive to manufacture. Gaskets also tend to leak after a relatively short period of time due to the expansion and contraction of the gasket itself due to temperature changes in the environment and exposure of the gasket material to the harsh cleaning chemicals used in many food service establishments.
Another prior art technique involves using a transparent polycarbonate material that is fused to the plastic cover by injection molding and mechanically mated with a glass or other transparent material. Due to the different amounts of thermal expansion and contraction experienced by its coacting elements (cover material, transparent material, glass) due to ambient temperature changes the elements deform. This results in warping, transforming, distorting, breaking, cracking, wrinkling, or otherwise transforming the elements. Additionally, no effective sealing-out of contaminants is provided. Unfortunately, due to the different rates of expansion and contraction of the different materials (cover material, transparent material, glass) a watertight seal can not be maintained and other techniques such as providing for the dissemination of spilled materials (i.e., drainage areas) are necessary in order to provide some form of spill resistance. Fluid dissemination beneath the cover entails use of additional materials and parts which can increase the cost of manufacture. Also such covers become more difficult to clean in that the cover must be removed to thoroughly clean the cover and underlying electronics. This further subjects the electronic components to remnants of the spills and harsh cleaning fluids.
Accordingly a need exists for a front cover assembly for a touch sensitive device that accommodates differential thermal expansion between elements and provides an effective liquid tight seal to protect against pollutants and spillage and that is readily attached to the touch sensitive device with which it is used.